Porous expanded polytetrafluoroethylene (hereinafter PTFE) materials are made as taught originally by U.S. Pat. Nos. 3,953,566 and 4,187,390 to Gore. These patents teach the manufacture of seamless, tubular forms of porous expanded PTFE by a process comprising extruding a preform of PTFE resin and a lubricant through a tubular extruder barrel having a male form aligned with the longitudinal axis of the tubular barrel, thereby creating a tubular extrudate, removing the lubricant from the tubular extrudate, expanding the tubular extrudate by stretching in a direction parallel to the longitudinal axis of the tubular extrudate at a temperature less than the crystalline melt point of PTFE, thereby forming a tube of porous expanded PTFE having a microstructure of nodes interconnected by fibrils. These porous expanded PTFE tubes have found application in the field of implantable vascular grafts. These are presently sold as GORE-TEX.RTM. Vascular Grafts (W. L. Gore & Associates, Inc., Flagstaff, Ariz.) and are in the form of tubes of porous expanded PTFE with an exterior reinforcement of a helical wrap of thin, porous expanded PTFE film to provide the grafts with increased hoop strength.
Present commercially available seamless tubes of porous expanded PTFE made by a process including extrusion typically have wall thicknesses of about 0.31 mm or greater. The present limitation on thinner walls is due to the extrusion and subsequent expansion process which is unable to produce these thinner walls with adequate concentricity and uniformity.
It is speculated that thinner-walled seamless tubes would be useful in certain vascular graft applications wherein the tube may serve as a replacement for segments of blood vessels. These include tubes of inside diameter less than about 2 mm. Thin-walled seamless tubes of even larger inside diameter may be useful as intraluminal vascular grafts and as coverings for intraluminal stents, both of which are used as luminal linings of body conduits.